Precise Time-Scaling of Gas Chromatographic Methods Using Method Translation and Retention Time Locking

Significance of the Topic

The accurate timing of peak elution is critical in gas chromatographic screening of complex samples, especially for pesticide residues and suspected endocrine disruptors. Method translation combined with retention time locking (RTL) enables laboratories to adapt a single capillary GC method across different detectors, instruments, speeds, and column formats while preserving retention order and minimizing revalidation effort.

Objectives and Overview of the Study

This work illustrates how Agilent’s method translation software and RTL tools were used to:

• Scale the HP RTL Pesticide Library method between GC-AED and GC-MS with a scale factor of 1
• Increase analysis speed threefold on the same GC-AED setup
• Adapt the method to a high-speed 0.1 mm id micro-ECD column at constant pressure

The goal is to extend the utility of an existing 567-compound pesticide screening method, reducing development time and ensuring precise retention time matching for library searching and confirmation.

Methodology

Method translation calculates new inlet pressure and oven ramp settings for a desired speed gain based on original column dimensions. RTL then uses calibration runs of a reference compound at several pressures to generate a retention time versus pressure curve. The steps are:

1. Define the scale factor (speed gain) in the translation software and enter original method parameters
2. Calculate translated inlet pressures and oven ramps for constant-pressure operation
3. Perform or predict RTL calibration runs to obtain locking pressures against target retention times
4. Export and scale the original retention time table by the factor
5. Import the new table and validate the scaled method with a standard mixture

Instrumentation

Analyses were performed on Agilent 6890 Series GC systems in constant pressure mode with:

• GC-AED detector (G2350A) controlled by GC-AED ChemStation
• 5973 MSD for GC-MS confirmation
• Micro-ECD detector for split 100:1 injections on a 0.1 mm id column
• HP-5MS capillary columns: 30 m×0.25 mm×0.25 µm and 10 m×0.1 mm×0.1 µm
• RTL software modules G2080AA and G2081AA

Main Results and Discussion

Scaling from GC-AED to GC-MS (scale factor 1) achieved retention time matching within ±0.1 minute for a 30 minute run. Predicted inlet pressures (17.93 psi) agreed with measured pressures after RTL calibration to within 0.03 psi (0.006 minute RT shift).

Increasing speed threefold on the same GC-AED platform reduced run times by a factor of three with acceptable resolution loss. RTL calibration pressures spanned only a 0.11 psi range (0.003 minute RT) demonstrating the method’s robustness.

Adapting the method to a 0.1 mm id micro-ECD column with 3× speed initially showed larger deviations due to assumed column length. Iterative adjustment of the column length in the translation software (from 10 m to 10.56 m) restored RT matching to within 0.03 minute, confirming the importance of accurate column dimensions for translations.

Benefits and Practical Applications

• Laboratories can reuse validated GC methods on different systems without full redevelopments
• Pesticide libraries remain consistent in retention time matching, streamlining library searches and reducing false positives
• Speed gains increase sample throughput while maintaining sufficient chromatographic separation for selective detectors
• Method translation and RTL integration yield predictable performance, improving method transfer between sites

Future Trends and Opportunities

• Integration of real-time method translation into instrument control software for automated scaling
• Expansion to new high-speed and low-thermal‐mass GCs enabling even faster analyses
• Application to emerging detectors and multidimensional GC methods
• Use of machine learning to predict optimal scale factors and calibration settings from historical data

Conclusion

Combining method translation with retention time locking offers a reliable framework for precise time scaling of capillary GC methods across instruments, detectors, and operational speeds. This approach maximizes the return on investment in method development, supports consistent library searching, and enables flexible adaptation to diverse analytical needs.

References

• Wylie PL, Quimby BD. A Method Used to Screen for 567 Pesticides and Suspected Endocrine Disrupters. Hewlett-Packard Application Note 228-402, 1998.
• Klee M, Giarrocco V. Predictable Translation of Capillary GC Methods for Fast GC. Hewlett-Packard Application Note 228-373, 1997.
• Giarrocco V, Quimby BD, Klee MS. Retention Time Locking: Concepts and Applications. Hewlett-Packard Application Note 228-392, 1997.
• Capillary Column Method Translator. Agilent user-contributed software. www.hp.com/go/mts.